Analysis of the Exposure Levels and Potential Biologic Effects of the PAVE PAWS Radar System (1979) / Chapter Skim
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'Biologic Effects Related to Exposure to Radiofrequency Waves'
'Biologic Effects Related to Exposure to Radiofrequency Waves'
Pages 42-78
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From page 42... ...
radiation are not limited to the PAVE PAWS radar, but pertain in general to all sources of such exposure. The inherent uncertainties in the evaluation of the biologic effects of microwave and other RF radiation are due in part to the absence of an adequate data base, especially with respect to the effects of chronic or long-term exposure to low radiation intensities.
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From page 43... ...
However, if a time-averaged exposure intensity of 1 mW/cm is used to differentiate high- from low-field intensity effects, the class of effects to be anticipated from exposure to PAVE PAWS radiation may be specified. The available theoretical and experimental data relative to the field intensities anticipated in areas of public access in the vicinity of PAVE PAWS suggest that effects in humans will be restricted to the class of low-intensity effects, inasmuch as exposures apparently will be at intensities less than 1 mW/cm .
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From page 44... ...
In view of the present limitations on the ability to assess the risks involved in human exposure to low-intensity microwave radiation, the approach used here in considering the potential exposure effects related to PAVE PAWS is to characterize, to the greatest extent possible, the anticipated exposures and to contrast these exposures with those encountered in other situations where humans are exposed to microwave or other RF radiation. In characterizing exposures to PAVE PAWS radar, all the factors that are shown to affect incident microwave exposure intensities and absorption in humans must be taken into account to provide an indication of the most probable degrees of exposure, as well as the maximal exposures (or "probable worst-case" situations)
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From page 45... ...
These physical factors are discussed here in the context of human exposure to radiation of the PAVE PAWS type, and then the information is applied to estimation of the dose that humans might absorb as a result of exposure to PAVE PAWS frequencies. Free-Space Irradiation The experimental condition that has been used in most studies is freespace irradiation of single animals.
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From page 46... ...
Electromagnetic Absorption in Humans and Animals in the Presence of Nearby Ground and Reflecting Surfaces QulY highly conducting (e.g., metallic sheet) ground and reflecting surfaces ' of infinite extent have been studied in attempts to determine absorption of electromagnetic waves in the presence of reflecting surfaces.
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From page 47... ...
At head resonance, the absorption cross section for the head region is approximately 3.0 times the physical cross section with a volume-average SAR that is about 3.3 times the SAR averaged 9Ygr the whole body. Both values greatly exceed numbers reports earlier '^ for spherical models of the isolated -47
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From page 48... ...
Table 13A describes SARs for free-space exposure conditions, and Table 13B for non-free-space conditions. Table 14 summarizes the results of calculations of the "probable worst-case" SARs predictable under conditions of exposure to PAVE PAWS radiation in buildings with unscreened windows facing the antenna, where field power density may be increased.
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From page 49... ...
in MHz = ll,400/Lcm, where Lcm is length in centimeters. fr = 65.2 MHz I I f_ = 82.6 MHz i L I I fr - 285 MHz From Equation 11, the whole-body averaged SAR = 0.0035 mW/g at 420 MHz 0.0033 mW/g at 450 MHz 0.0061 mW/g at 420 MHz 0.0057 mW/g at 450 MHz 0.016 mW/g at 420 MHz 0.015 mW/g at 450 MHz Deposition rates 5-10 times higher than whole-body average SARs are expected for the neck, the legs, and the elbows for these irradiation conditions.
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From page 50... ...
Smaller increases are expected for imperfectly reflecting surfaces. Even though enclosed structures, such as rooms, have not been studied at length, field increases by factors of some 5-10 have been reported, presumably owing to reflections from walls, of electromagnetic energy coupled in from windows.
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From page 51... ...
1.38-m 10-yr-old I 3.5-kg, 0.4 m man I child I infant I I Whole-body-averaged SAR 435 MHz, corresponding to average PAVE PAWS frquency: I I 7.5x0.0034= I 7.5 x 0.0059 = 0.044 mW/g I 7.5x0.0155= 0.026 mW/g I 0.12 mW/g SAR at hot spots: I I =0.26 mW/g | -0.44 mW/g | -1.16 mW/g Head-averaged SAR: I I :7.5 x 0.0175 = -7.5 x 0.012 = 0.09 mW/g -7.5 x 0.0108 0.13 mW/g j I 0.08 mW/g SAR at hot spots in the head: I I = 0.66 mW/g "0.47 mW/g -0.4 mW/g aField increase by factor of 7.5 assumed in these calculations. Such a factor is likely to be among highest that may be encountered in buildings.
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From page 52... ...
3.32 mW/g Local values Brain metabolic rate 11 mW/g Heart-muscle metabolic rate 33 mW/g LOCALIZED POWER ABSORPTION DUE TO ATTACHED INSTRUMENTATION AND IMPLANTS When conducting objects, wires, or electrodes (such as surgical pins or pacemakers) are brought into contact with or implanted in biologic tissues exposed to electromagnetic fields, high-intensity fields may be induced locally where the conductors contact tissue.
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From page 53... ...
Thus, the presence of the wire results in large SAR intensification at the point of contact. The SAR increase due to metallic implants in tissues may be illustrated by considering the conducting prolate spheroid with major axis L and minor axis 2a imbedded in tissue in the presence of an electric field.
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From page 54... ...
The report indicated that, with design lmprovements in the newer models, the interference problem should be eliminated. However, older, maximally susceptible pacemakers may be affected by exposure to PAVE PAWS radiation fields, especially near the exclusion area, where instantaneous field strengths in excess of 10 V/m may be encountered.
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From page 56... ...
Electroencephalographic Alterations Both acute and chronic exposures to microwave fields have been reported to change EEG patterns in humans and animals. According to Baranski and Edelwejn, technicians repeatedly exposed to presumed highlevel fields in radar-repair shops may eventually exhibit flat EEG records associated with subjective complaints of headaches and copious sweating, but no precise data on field characteristics are available.
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From page 57... ...
diminished sensitivity to audiogenlc seizures in rats exposed for 4 h a day for the first 10 weeks of life. A distinction should be drawn between microwave fields that appear to influence brain-tissue excitability directly and fields that are sufficiently intense to induce thermal stress.
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From page 58... ...
Both western and eastern European studies have therefore focused on possible effects of chronic exposure to low-intensity microwaves on responses to neurotropic drugs that have effects on specific classes of transmitter substances.
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From page 59... ...
Pulse rates of the microwave fields were either 20 or 1,000 pulses/s, and field intensities ranged from 0.5 to 10 yW/cm . Cholinesterase activity dropped by almost half during 50-MHz, 10 yW/cm exposures 90-120 days after the beginning of exposure.
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From page 60... ...
found that rats exposed to 500 yW/cm , 2,450-MHz CW fields T"h7day for 3 months showed initial decreases in blood chollnesterase, and then a return to control values. The isolated rat heart was slowed (bradycardia)
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From page 61... ...
Increased calcium efflux was maximal for field intensities around 1.0 mW/cm2 in the studies at 147 MHz by Blackman £t al. and at 450 MHz in the studies by Bawin et al.
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From page 62... ...
The estimated energy-flux densities of an incident 2,450-MHz plane wave that would result in an energy-absorption rate of 1 mW/g lie between 2 and 6 mW/cm and would depend on the animal's absorptive cross-sectional area and its orientation with respect to E and H vectors of the incident field.57 Perceptual thresholds for short-duration pulsed microwave fields have not been reported, although early reports ' revealed that human beings can readily hear a train of pulses at peak flux densities near 100 mW/cm and averaged densities near 50 ji W/cm . The RF-hearlng effect is believed to result from thermoelastic expansion; i.e., a microwave pulse that rapidly (rise time in microseconds)
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From page 63... ...
Escape of sorts does occur in pulsed fields, " but the behavior of the albino rat near a threshold of averaged flux density approximating 800 y W/cm is not permanent withdrawal, but a shift of preference in which the animal with a choice spends more time away from the field than in it. But frequent reentry by the animal into the field does occur.
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From page 64... ...
. Stimulation of the HPT system resulting in an increase in thyroxine content occurs at power densities that result in measurable increases in body temperature.
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From page 65... ...
Whether GH decrease is an acute response or a prolonged sequela of microwave exposure is an unanswered question, but one of considerable interest, in the light of conflicting reports that decreased or even increased body mass is a consequence of acute or chronic in utero exposure to microwaves. The lowest power density at which endocrinologic changes have been reported in the eastern literature is 1 mW/cm ; serum thyroxine was transiently increased in irradiated, but not in sham-irradiated, rats after a 4-h treatment with 2,450-MHz microwaves.l01 In none of the studies cited were irreversible changes observed, but the dearth of endocrinologic assays of animals that undergo truly longterm exposures to microwaves or other RF radiation precludes assessment of chronic effects of fields of low power density (less than 1 mW/cm )
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From page 66... ...
The finding of shifts in the circadian rhythm of the blood-forming system at power densities near 1 mW/cm is a physiologic indicant of responsiveness to relatively weak microwave fields. A similar phase shift in the circadian rhythm of body temperature was observed by Lu et^ _al.
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From page 67... ...
In general, accurate reconstruction of the exposure conditions that have resulted in cataract induction has not been possible. Thus, there is some uncertainty in the interpretation of the ocular effects of microwave exposure.
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From page 68... ...
Furthermore, the radiation fields produced by the many different microwave sources in given work environments are often generalized into expressions of averaged power density, without reference to the radiation frequency or waveform. The difficulty of applying such generalized information to the specific environmental radiation conditions produced by PAVE PAWS becomes immediately apparent.
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From page 69... ...
However, a major difficulty with these studies is the lack of specification of the modulation characteristics of the microwave sources. The low-intensity pulsemodulated radiation from the PAVE PAWS radar is of primary interest here, and the direct applicability of the Soviet studies to PAVE PAWS is questionable.
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From page 70... ...
12 Baranski and Czerski report on a study of several thousand Polish microwave workers who received low, moderate, and high exposures to microwave radiation. The group exposed to low power densities (average, tens of microwatts per square centimeter)
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From page 71... ...
However, the incidence of the reported functional disturbances was related to the age of the workers. The findings of these studies do not support the hypothesis of cumulative effects of microwave exposure with increasing duration of exposure, at power densities up to 6 mW/cm .
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From page 72... ...
, with the highest power density between 2 and 3 GHz. The medical records of a group of U.S.
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From page 73... ...
A number of individual case histories of microwave induction of cataract have been reported, '' but in no case, is there reason to suspect that the exposures were not well in excess of 100 mW/cm . One study of possible relevance to PAVE PAWS hints at a lessening of cataractogenic efficiency at the comparatively low frequencies used in the investigation of cataract induction -- 200, 385, and 468 MHz.
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From page 74... ...
One Eastern European study of long-term exposure of workers to power densities at or below 1 mW/cm concluded that such exposure does not result in any "reliable deviations of ocular sensitivity." CARDIOVASCULAR EFFECTS Edelwejn et^ a^. concluded in 1974 that no serious cardiovascular disturbances had ever been produced in man or experimental animals by exposure to microwave radiation.
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From page 75... ...
GONADAL EFFECTS 93 One report " claimed that 22 of 31 microwave technicians experienced loss of libido and reduced spermatogenesls after an average of 8 yr of exposure to microwave radiation frequencies between 3.6 and 10 GHz at power densities ranging from tens to hundreds of microwatts per square centimeter. Both libido and spermatogenesis returned to normal in most of the technicians 3 months after cessation of microwave exposure.
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From page 76... ...
power density reflects earlier times, when the biologic importance of modulated signals was relatively unappreciated. Therefore, it may be concluded that most of the available information on human effects has questionable applicability to PAVE PAWS.
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From page 77... ...
Although lenticular changes have been discovered in groups of microwave workers, a cause-and-effect relationship between the reported defects and microwave radiation has not been conclusively demonstrated. Considering the radiation frequency and expected power densities associated with PAVE PAWS, the possibility of induction of cataracts in exposed members of the public is very small.
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From page 78... ...
There is no evidence of a cumulative effect on humans, but the question is unresolved. Taking the literature on reported human effects as a whole and considering the nature and weight of available evidence, as well as the limitations of the investigative techniques used, the Panel believes that the probability of adverse biologic effects on persons exposed to radiation from PAVE PAWS is very low under normal operating conditions and that such effects would be expected to be subtle, transient, and reversible.
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